Messages in this thread | | | Date | Thu, 29 Feb 2024 12:20:18 +0300 | Subject | Re: [PATCH net] gtp: fix use-after-free and null-ptr-deref in gtp_newlink() | From | Vasiliy Kovalev <> |
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Hi,
29.02.2024 02:51, Pablo Neira Ayuso wrote: > On Wed, Feb 28, 2024 at 02:47:03PM +0300, Alexander Ofitserov wrote: >> The gtp_link_ops operations structure for the subsystem must be >> registered after registering the gtp_net_ops pernet operations structure. > > A fix for this was already applied, see: > > commit 136cfaca22567a03bbb3bf53a43d8cb5748b80ec > Author: Vasiliy Kovalev <kovalev@altlinux.org> > Date: Wed Feb 14 19:27:33 2024 +0300 > > gtp: fix use-after-free and null-ptr-deref in gtp_genl_dump_pdp() > >> diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c >> index 2129ae42c7030..0ddec4cc84093 100644 >> --- a/drivers/net/gtp.c >> +++ b/drivers/net/gtp.c >> @@ -1903,26 +1903,26 @@ static int __init gtp_init(void) >> >> get_random_bytes(>p_h_initval, sizeof(gtp_h_initval)); >> >> - err = rtnl_link_register(>p_link_ops); >> + err = register_pernet_subsys(>p_net_ops); >> if (err < 0) >> goto error_out; > > BTW, I like that this calls register_pernet_subsys() before > rtnl_link_register(), where a rtnetlink request could come before > pernet is set up. > >> - err = register_pernet_subsys(>p_net_ops); >> + err = rtnl_link_register(>p_link_ops); >> if (err < 0) >> - goto unreg_rtnl_link; >> + goto unreg_pernet_subsys; >> >> err = genl_register_family(>p_genl_family); >> if (err < 0) >> - goto unreg_pernet_subsys; >> + goto unreg_rtnl_link; >> >> pr_info("GTP module loaded (pdp ctx size %zd bytes)\n", >> sizeof(struct pdp_ctx)); >> return 0; >> >> -unreg_pernet_subsys: >> - unregister_pernet_subsys(>p_net_ops); >> unreg_rtnl_link: >> rtnl_link_unregister(>p_link_ops); >> +unreg_pernet_subsys: >> + unregister_pernet_subsys(>p_net_ops); >> error_out: >> pr_err("error loading GTP module loaded\n"); >> return err; >> -- >> 2.42.1 >> >>
This patch fixes another problem, but a similar one, since the sequence is incorrect when registering subsystems.
Initially, the registration sequence in the gtp module was as follows:
1) rtnl_link_register();
2) genl_register_family();
3) register_pernet_subsys();
During debugging of the module, when starting the syzkaller reproducer, it turned out that after genl_register_family() (2),
without waiting for register_pernet_subsys()(3), the .dumpit event is triggered, in which the data of the unregistered pernet subsystem is accessed.
That is, the bug was fixed by the commit
136cfaca2256 ("gtp: fix use-after-free and null-ptr-deref in gtp_genl_dump_pdp()") [1]
and the registration sequence became as follows:
1) rtnl_link_register();
2) register_pernet_subsys();
3) genl_register_family();
However, syzkaller has discovered another problem:
after registering rtnl_link_register, the .newlink event is triggered, in which the data of the unregistered pernet subsystem is accessed.
This problem is reproducible on current stable kernels and the latest upstream kernel 6.8-rc6, in which the patch 136cfaca2256 [1] is applied.
Therefore, the correct sequence should be as follows:
1) register_pernet_subsys();
2) rtnl_link_register();
3) genl_register_family();
The proposed patch is developed on top of the commit changes [1], does not conflict with it and fixes the described bug.
[1] https://lore.kernel.org/lkml/20240220160434.29bcaf43@kernel.org/T/#mb1f72c2ad57b7ea6d47333e8616beccf8bce0e23
-- Regards, Vasiliy Kovalev
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